The role of cyclic adenosine monophosphate (C-AMP) and cyclic guanosine monophosphate (C-GMP) in capacitiation and the acrosome reaction will be investigated in guinea pig sperm to determine the relationship of these substrates to these physiological states. Levels of C-AMP and C-GMP will be determined by radioimmunoassay analysis of epididymal, capacitated and fertilizing (acrosome reacted) sperm in vitro. The effects of nucleotides on these stages of the sperm life cycle will be monitored by the addition of C-Amp and C-GMP to the respective media. Correlative fine structural localization of adenyl and guanyl cyclase and phosphodiesterase will be carried out on experimental and control incubated sperm. The effect on the sperm surface of these media, with and without added substrate, will be studied utilizing fine structural markers for plasma membrane receptors.